Valves and valve systems are used to control pressure within containers and flow into and out of containers. For example, vacuum relief valves are used to control the pressure within a storage vessel such that the negative pressure differential between the storage vessel and the ambient atmosphere is not too large. In this regard, vacuum relief valves permit ambient gas to enter the storage vessel when the pressure within the storage vessel falls below the ambient pressure by a specified amount. The pressure differential can result from a number of factors, including, but not limited to, temperature changes of the vessel or contents, changes in size of the vessel, removal of some or all of the contents of the vessel and other factors. This under-pressure or vacuum can be dangerous and can lead to implosion or damage to the vessel.
Such valves and valve systems can be utilized in a number of applications. For example, these valve systems are often used in rail cars, ISO tanks, tote tanks and other storage vessels for transporting fluids, including liquids and/or gas. Generally, it is preferred to prevent the lading or contents of the tank from contacting or building up on the valve. Particularly, it is often preferred to prevent the lading from contacting the valve seal and/or valve seat to prevent deterioration of the valve seal and seat. Such deterioration can result depending on the type of lading, including, but not limited to corrosive fluid, acidic fluids and the like.
Furthermore, as vacuum relief valves permit ambient gases to enter the vessel under certain conditions, it is preferred to prevent unwanted material from entering the vessel along with the ambient gas. For example, in the case of a railroad tank car, the vessel may be transported around the country between dusty locations and locations having numerous insects where these particles can be sucked into the vessel along with the ambient gas. In this example, it is preferred to prevent the dust and insect from entering and possibly contaminating the lading or otherwise interfering with the operation of the valve.
Additionally, conventional vacuum relief valves oftentimes are prone to malfunction due to age and/or use. For example, the valve stem can become damaged if it is not adequately supported. In this regard, the valves can be serviced to replace and/or maintain the components of the valve. However, if this servicing is not performed properly by a qualified technician, the valve may fail, thereby possibly leaking dangerous materials out into the ambient atmosphere. Therefore, it would be preferred to have some form of security measure to prevent or deter unqualified servicing of the valve or otherwise provide some sort of indication that unqualified servicing had occurred.